As one of conventional capacitance type humidity sensors as a physical quantity sensor manufactured by interposing a humidity sensitive film whose relative dielectric constant is changed in response to humidity between one pair of electrodes. This type of sensor is disclosed in, for example, Japanese Laid-open Patent Application No. 2002-243690, which corresponds to U.S. Pat. No. 6,580,600 and US 2002-0114125A1.
The capacitance type humidity sensor has been manufactured by that one pair of electrodes are formed in such a manner that the one-paired electrodes are separated from each other and are located opposite to each other on the same plane of a semiconductor substrate, and a humidity sensitive film is formed on the semiconductor substrate in such a manner that the humidity sensitive film covers the one-paired electrodes, and a space between the one-pared electrodes. The relative dielectric constant of the humidity sensitive film is changed in response to humidity. Also, while an insulating film (second insulating film) has been formed between the electrodes and the humidity sensitive film, a humidity resistive characteristic as to the electrodes may be secured by this insulating film. As a consequence, even if an expensive metal having a superior humidity resistive characteristic such as a noble metal is not especially used, these electrodes can be manufactured by employing such a material, for instance, aluminum (i.e., Al), which can be used in a normal semiconductor manufacturing line.
Also, a circuit unit (circuit element unit) for processing a capacitance change between the electrodes so as to obtain an electric signal has been provided on the side of a plane of a semiconductor substrate, on which the electrodes are formed. If a wiring material employed in this circuit unit is the same as the structural material of the electrodes, then manufacturing steps may be made simple.
On the other hand, in the capacitance type humidity sensor having the above-described structure, in order to protect pads (namely, to prevent corrosion) which may function as external connection terminals provided at least on an edge portion of the circuit unit, surfaces of these pads must be covered by such a protecting material as gel, or the like.
However, both the electrodes and the circuit unit have been formed in an integrated manner on the same plane side of the semiconductor substrate. Also, it is practically difficult to locally coat the gel. As a consequence, the entire surface of the circuit forming plane of the semiconductor substrate is covered by the gel, and the upper portion of the detecting unit made of both the electrodes and the humidity sensitive film is also covered by the gel, so that the response characteristic of the capacitance type humidity sensor is deteriorated.
Also, other than the above-explained structure, another capacitance type humidity sensor having the following structure is known. That is, while a detection board having a detecting unit whose capacitance is changed by humidity and a circuit board having a circuit unit are separately prepared, sensor pads electrically connected to electrodes via a bonding wire, or the like, are electrically connected to the circuit units in this capacitance type humidity sensor. However, also, in this case, since the sensor pads of the detection board must be covered, both the humidity sensitive film and the upper portion of the electrodes are covered by the gel, so that the response characteristic of the capacitance type humidity sensor is deteriorated.
The above capacitance type humidity sensor has been manufactured by that one pair of electrodes are formed in such a manner that the one-paired electrodes are separated from each other and are located opposite to each other on the same plane of a substrate, and a humidity sensitive film is formed on the substrate in such a manner that the humidity sensitive film covers the one-paired electrodes, and a space between the one-pared electrodes. The relative dielectric constant of the humidity sensitive film is changed in response to humidity.
In this case, in a manufacturing operation of the above-described capacitance type humidity sensor, if paste containing a polymer material corresponding to a structural material is screen-printed, and then, the printed paste is hardened so as to form a humidity forming film, then a patterning process by a photo-process required in such a case that a spin coat method is applied can be eliminated. In other words, the manufacturing steps can be simplified. Also, there is another merit that the apparatus can be easily handled.
On the other hand, in the screen printing operation, since the paste is printed on the substrate via the pattern holes formed in the screen mask, the screen mask must be correctly positioned with respect to the substrate. Also, in the above-explained capacitance type humidity sensor, the high positioning precision of the humidity sensitive film is necessarily required in connection with, especially, the compactness of the sensor build, so that the screen mask must be correctly positioned with respect to the substrate.
To this end, conventionally, when a screen mask is positioned with respect to a substrate, for example, the screen mask abuts against a dummy substrate (namely, test-purpose substrate) and paste is screen-printed. Then, a position of a printing area which has been printed through pattern holes is detected by employing an imaging apparatus such as a CCD camera. Then, the substrate is positioned on a stage in order that the detected printing area and the area which is wanted to be printed may become substantially same positions. Under this positioning condition, a printing operation is carried out.
However, in the case of screen printing operations, it is practically difficult to uniform thicknesses of humidity sensitive films. This reason is caused by that, for instance, a so-called “saddle” phenomenon occurs in edge areas. As a consequence, in order that effective areas of center portions (which are surrounded by edge portions) whose film thicknesses become substantially uniform are arranged in such areas on substrates, which are wanted to be printed, pattern holes have been set to be larger than the areas which are wanted to be printed. Also, in the case of screen printing operations, since squeezes are slid so as to print paste, shapes and/or dimensions of areas (humidity sensitive films) which have been actually printed are more or less different from pattern holes. In other words, there are large differences in the shapes and/or dimensions between the area on the substrate which is wanted to be printed, and the area which has been actually printed on the dummy substrate. Thus, even when the positioning operation of the substrate is carried out while the printed area is employed as the reference area, there is such a problem that the humidity sensitive film cannot be formed in high positioning precision.
The above capacitance type humidity sensor has been manufactured by comprising a semiconductor substrate; a first insulating film formed on the semiconductor substrate; one pair of electrodes; a second insulating film formed in such a manner that the second insulating film covers one pair of the electrodes; and a humidity sensitive film formed on the second insulating film in such a manner that the humidity sensitive film covers one pair of the electrodes and a space between the one-paired electrodes. The one-paired electrodes have been formed on the first insulating in such a manner that these one-paired electrodes are separately located opposite to each other on the same plane. As a result, while the humidity sensitive film whose relative dielectric constant is changed in response to humidity has been interposed between one-pair of the electrodes, the humidity can be detected based upon the change in the relative dielectric constants of the humidity sensitive film.
The conventional capacitance type humidity sensor is arranged by that the detecting unit constituted by the electrodes and the humidity sensitive film is formed on a rigid substrate, e.g., the semiconductor substrate and the glass substrate.
As a consequence, in such a case that the above-explained conventional capacitance type humidity sensor is directly arranged on a mounting unit having a curved plane, since this conventional capacitance type humidity sensor is partially made in contact to the mounting unit, there is a risk that the humidity sensor is broken when external force is applied to this sensor. For instance, the conventional capacitance type humidity sensor is arranged on a windshield of a vehicle in order to be applied to an automatic control operation of an automatic air conditioning system as one of purposes capable of preventing a fogging phenomenon of the windshield of the vehicle.
Also, such a sensor arrangement may be conceived. That is, the conventional capacitance type humidity sensor is arranged on the mounting unit via a buffering member which owns a curved plane formed in correspondence with the curved plane of the mounting unit. In this sensor arrangement, the build of the sensor containing the buffering member becomes large. As a consequence, in particular, when the humidity sensor is mounted on the windshield, this humidity sensor may disturb viewing fields of passengers of the vehicle, resulting in unfavorable results.
Under such a circumstance, the conventional capacitance type humidity sensor has been arranged on a flat unit (for example, on dash panel) which is separated from the mounting unit having the curved plane. As a consequence, errors with respect to a portion which is actually wanted to be measured may be more or less produced.
Conventionally, there are main two different types of humidity sensors, a resistance type humidity sensor and a capacitance type humidity sensor. In view of these conventional humidity sensors, the inventors have preliminary studied a capacitance type humidity sensor as a prototype having a structure shown in FIG. 16.
FIG. 16 indicates a sectional structure of this capacitance type sensor. As indicated in this drawing, an insulating film J2 is formed on a front surface of a semiconductor substrate J1, and also, a plurality of electrodes J4 which are divided by a plurality of trenches J3 are formed on the front surface thereof. The internal portions of the plural trenches J3 are filled with humidity sensitive materials J6 via insulating films J5 which are formed on the front surfaces of these plural electrodes J4.
In the humidity sensor having the above-described structure, since a dielectric constant “∈” of each humidity sensitive member J6 is varied in response to humidity within an atmosphere, capacitances which are formed among these plural electrodes J4 are changed. As a result, this humidity sensor may detect humidity based upon a variation of electric signals in response to the capacitance change. This is disclosed in, for example, Japanese Laid-open Patent Application No. 2002-243689, which corresponds to U.S. Pat. No. 6,445,565-B1.
In the humidity sensor having the above-described structure, electric signals are outputted which respond to the capacitances formed among the plural electrodes J4, so that these electric signal outputs become analog outputs. Therefore, the analog outputs of the humidity sensor must be converted into digital outputs. To this end, an A/D converter is required. As a result, there is such a problem that the circuit arrangement of the humidity sensor becomes complex, and thus, the humidity sensor cannot be made compact.
It should be understood that although the description has been made of the humidity sensor as an example, a similar problem may occur in sensor apparatus for instance, infrared sensors, pressure sensors, which employ the above-explained operating mode.